package ch.sharpsoft.quaternion.v1;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.ShortBuffer;

import android.opengl.GLES20;

public class Square {

	private final String vertexShaderCode =
	// This matrix member variable provides a hook to manipulate
	// the coordinates of the objects that use this vertex shader
	"uniform mat4 uMVPMatrix;" +

	"attribute vec4 vPosition;" + "void main() {" +
	// the matrix must be included as a modifier of gl_Position
			"  gl_Position = vPosition * uMVPMatrix;" + "}";

	private final String fragmentShaderCode = "precision mediump float;"
			+ "uniform vec4 vColor;" + "void main() {"
			+ "  gl_FragColor = vColor;" + "}";

	private final FloatBuffer vertexBuffer;
	private final ShortBuffer drawListBuffer;
	private final int mProgram;
	private int mPositionHandle;
	private int mColorHandle;
	private int mMVPMatrixHandle;

	// number of coordinates per vertex in this array
	static final int COORDS_PER_VERTEX = 3;
	static float squareCoords[] = //
	       { -0.5f, 0.5f, 0.0f, // top left
			-0.5f, -0.5f, 0.0f, // bottom left
			0.5f, -0.5f, 0.0f, // bottom right
			0.5f, 0.5f, 0.0f }; // top right

	private final short drawOrder[] = { 0, 1, 2, 0, 2, 3 }; // order to draw
															// vertices

	private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per
															// vertex

	// Set color with red, green, blue and alpha (opacity) values
	float color[] = { 0.2f, 0.709803922f, 0.898039216f, 1.0f };

	public Square() {
		// initialize vertex byte buffer for shape coordinates
		ByteBuffer bb = ByteBuffer.allocateDirect(
		// (# of coordinate values * 4 bytes per float)
				squareCoords.length * 4);
		bb.order(ByteOrder.nativeOrder());
		vertexBuffer = bb.asFloatBuffer();
		vertexBuffer.put(squareCoords);
		vertexBuffer.position(0);

		// initialize byte buffer for the draw list
		ByteBuffer dlb = ByteBuffer.allocateDirect(
		// (# of coordinate values * 2 bytes per short)
				drawOrder.length * 2);
		dlb.order(ByteOrder.nativeOrder());
		drawListBuffer = dlb.asShortBuffer();
		drawListBuffer.put(drawOrder);
		drawListBuffer.position(0);

		// prepare shaders and OpenGL program
//		int vertexShader = GLRenderer.loadShader(GLES20.GL_VERTEX_SHADER,
//				vertexShaderCode);
//		int fragmentShader = GLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,
//				fragmentShaderCode);

		mProgram = GLES20.glCreateProgram(); // create empty OpenGL Program
//		GLES20.glAttachShader(mProgram, vertexShader); // add the vertex shader
//														// to program
//		GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment
//															// shader to program
		GLES20.glLinkProgram(mProgram); // create OpenGL program executables
	}

	public void draw(float[] mvpMatrix) {
		// Add program to OpenGL environment
		GLES20.glUseProgram(mProgram);

		// get handle to vertex shader's vPosition member
		mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");

		// Enable a handle to the triangle vertices
		GLES20.glEnableVertexAttribArray(mPositionHandle);

		// Prepare the triangle coordinate data
		GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX,
				GLES20.GL_FLOAT, false, vertexStride, vertexBuffer);

		// get handle to fragment shader's vColor member
		mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

		// Set color for drawing the triangle
		GLES20.glUniform4fv(mColorHandle, 1, color, 0);

		// get handle to shape's transformation matrix
		mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");

		// Apply the projection and view transformation
		GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);

		// Draw the square
		GLES20.glDrawElements(GLES20.GL_TRIANGLES, drawOrder.length,
				GLES20.GL_UNSIGNED_SHORT, drawListBuffer);

		// Disable vertex array
		GLES20.glDisableVertexAttribArray(mPositionHandle);
	}
}